A PLUG-IN MINIELECTRODE FOR MEASUREMENTS IN STIRRED PHOTOMETRIC CUVETTES

A device is described to perform potentiometric measurements with ion- sensitive electrodes in stirred photometric cuvettes, Its design allow s to make additions to the reaction medium with microliter syringes du ring measurements. Originally, this plug-in electrode was designed to register the free Ca2+ concentrations in the incubation medium of mito chondrial suspensions during measurements of the free matrix Ca2+ conc entration with a permeant fluorescent Ca2+ indicator. However, numerou s other applications can be easily realized, such as the combination o f mitochondrial light-scattering measurements and ion-transport measur ements, the combination of the permeabilized cell technique with fluor escence measurements of intracellular organelles or simply the calibra tion of the fluorescence of Ca2+ indicators with a Ca2+ ion-sensitive minielectrode. Compared with the use of a second fluorescent indicator the use of an electrode has the advantage that the signal can be tran sformed into ion concentrations already during the measurements.